Prevention of foaming in steam generation



Patented Sept. 2, 1952 PREVENTION OF FOAMING IN STEAM GENERATION Carl E. Johnson, Westchester, 111., assignor to: National Aluminate Corporation, Chicago, 111., a corporation of Delaware No Drawing. Application August 14, 1948, Serial No. 44,392

The present invention relates to improved antifoaming compositions which are added to water that is subjected to boiling, as in the boilersoflocomotives, stationary steam generators, evaporators, and in other instances where the boilingof water occurs, especially under superatmospheric temperature and pressure conditions, whereby the tendency of the water therein to foam is prevented or reduced and the boiling characteristics of the water so improved that priming of the steam generator and carryover of boilerv water; with, the steam therefrom. isprevented. i It is well known that, in the operation of steam boilers, such as in railroad locomotives, in electric power plants and the= likehor in other boilingpperationswhere steam is formed, as for example in, evaporators, that the water therein, even; though initially it shows little tendency to foam, will when th amount of total dissolved solids approaches a relatively high concentration due to the productiontofsteam, develop a very decided tendency to foam. .This foaming of the water in a boiler producing steamis characterized-notonly by aniaccumulationof relatively stable froth or foam on the surface. of the boiler water but. also by the formation at, the heat transferisurfacesin the boiler of extremely small steambubbles. These minute bubbles show almost no tendency to coalescean'd theresult is that the entire volume of water inthe steam generator is lifted in the form; of so-called light Water, which is actually an intimate mixture of boiler water and tiny steam bubbles. When this occurs, considerable quantities of boiler water are physically carried out of the boilers or evaporators with the steam, thereby introducing solid matter into the steam lines and into the eventual condensate. Such carryover has many disadvantages because it tends to contaminate and restrict the steam lines, to plug or corrode the valves, todeposit on turbine blades, to plug. and cause burning out of superhe'ater tubes, and under serious conditions may evenimpair the cylinders and piston rods of steam engines or otherwise render the steam unfit for use. The carryover is frequently due in part, at least, to priming, or what may be describcdlassurging or boiling over of. the Water.

Attemptshave been made in the past to controlfoaming and priming by controlling the dissolvedfsolids content of the water as by excessive blow down of the boiler, that is, the removal,

either continuously or periodically, of a portion of theboiler water. containing theundesired ex- 16 Claims. (crest-321) cess solids. Also, itihas been common to addm aterials for the purpose of abating the foam as by the injection of such. materials as castor oil; tallow, andthe like. While these fatty materials, notably castor oil, have some small degree of efficiency, they are, on the other hand, quite deficient in that they introduce new dimculties which, in some instances, are worse than the conditions. they are intended to cure. In the first place, these fatty materials or glycerides are very unstable under severe'hydrolytic' conditions encountered in steamgeneration, particularly der the conditions of superatmospheric pressure, the'corresponding high temperatures and the ale kalinity of the boiler water. The resultantldecomposition products which remain in the boiler tend to increase the foaming tendencies ofthe boiler water and'to' accumulate in such a way as to give a compound dirty boiler, necessitating frequent washing. Furthermore, in many instances certain of the decomposition products thus produced, or sometimes even the materials themselves, have a definite volatility with steam and will, therefore, steam-distill out of the steam generators, thus appearing in the steam and. in the eventual condensate. This, of course, is also undesirable; Additiona1ly,. such types of anti foaming agents usually are of sucha low order of efficiency that they have to be employed-in relatively large quantities, adding not on1y to the expense but also to the inconvenienceof. operat-- ing the steam generators; and since they are so unstable their effectiveness is of shortduration, necessitatingthe continual charging intQ the boil-. ersor other steam generators of relatively large amounts of these older antifoa'mi'ngagents...

The mostnote-worthy advance oven the use-of the fatty glycerides described-above was the dis-- covery and development of certain highmolecu lar weight substituted polyamides, which antifoaming compounds overcame many of the disadvantages of the former, especially in that they were highly efiicient at lower dosage levels and much more resistant todecomposition, s -that their efiective life was relatively greater, jI

One of the objects of this invention is toprot: vide a new and improved process. for preventing the foaming and priming of steam generators, thus improving thequality bfthe steam produced thereby.

Another object is to provide new and improved compositions for adding-to the water in a steam fienerator to prevent or reduce its tendency to Another object is to provide antifoaming comtive ingredients are readily soluble in water at 1 relatively low temperatures, (e. g. '75 degrees F.) I but decrease in solubility when the water is heated to relatively high temperatures such as are employed in the generation of steam under super-,

atmospheric pressures and the. corresponding temperatures.

Still another object of invention is to provide a process of generating steam and new andim I proved antifoam compositions therefore wherein the period of effectiveness of the antifoam composition is greatly prolonged as compared to the periodof-eifectiveness of other antifoamcompositions presently known in the art. still another object of the invention is to provide anew and improved process of inhibiting foaming during steam generation which permits operations at higher dissolved solids contents than has heretofore been'considered possible.

An-additional object is to provide new and useful antifoaming compositions of an extremely high order of resistance to decomposition under the-conditions prevailing in steam generation. Other objects will appear hereinafter.

In accordance with this invention, it'has now beendiscovered that there is a series of compounds that are very effective when used as antifoaming and antipriming agents in steam generators and which may be broadly designated as high molecular weight diethers 0f polyoxyalkylene glycols, characterized by the presence in the polyoxyalkylene chain 'of one or more oxymethylene groups. These diethers'possess several importantadvantages over formerly known antifoam compositions. They are all much more effective than any of the fatty glycerides, and manyare more eifective than any hitherto known material s. Furthermore, they are much more stable to decomposition under conditions of use than'any of the glycerides or polyamides, thus giving them a greatly prolonged period of effectiveness in preventing foaming. In general, they are more'readily dispersed in the water being fed to the steam generator than are older materials, and a further advantage offered by many of these diethers is that they are liquids or very low-melting waxy materials which are readily soluble at ordinary temperatures.

{The diethers preferably employed in the practice of this invention may be represented by the structural formula and X is apolyoxyalkylene chain selected from the group consisting of:

wherein. E is hydrogen or an alkylor aryl radi- 4 cal, n is an integer equal to 2 or more, and mai have several values in the same compound, a: and z are integers of 2 or more, and y is an integer of 1 or more. Such compounds are thus seen to include diethers of polyoxyalkylene glycols, in thepolyoxyalkylene chain-"of which appears at leastione.oxymethylene group, and iniwhich there are also other (larger) oxyalkylene groups. By

,pthese larger oxyalkylene groups is meant oxyalkylene groups which are not oxymethylene. Examples of these larger oxyalkylene groups are oxyethylene (-OCH2CH2), oxypropylene H Hi I 230 and oxyalkylenes of greater number of carbons such as oxypentamethylene, oxyhexamethylene, oxydecamethylene and higher homologues. The larger oxyalkylene groups present in the polyoxyalkylene chainmay all be the same, or-they may be'diiferent, so that several are present in the same chain. When the larger oxyalkylene groups are not all the same, they may occur in the chain in various proportions and in a random or irregular sequence, with respect to each other.

In order that these diethers of polyoxyalkylene glycols possess the property of efii ciently preventing the foaming and'priming' of steam generators', they should be of relatively high mo-'- lecular weight. The lower limiting value of molecular weight will vary somewhat'with variations in the size of the terminal groups R and R and with the nature of the oxyalkylene'groups comprising the polyoxyalkylene chain, as explainedmore fully hereinafter, but will, in general, be intermediate between 500 and 1000.

As pointed out above, all of the materials em ployed in the practice of this invention have the common feature of being diethers of polyoxy' alkylene glycols, in the polyoxyalkylene chain of which one or more unsubstituted oxymethylene, or substituted oxymethylene, groups occur. For

, purposes of more detailed discussion, however, it

will be convenient to consider these diethers under four separate classifications.

The first classification which may be con-' sldered consists of the diethers having the general structural formula wherein the symbols R, R, E, n, x, and y have the same significance assigned to them hereinbefore, with the additional provision that y may also be zero, in which case the general structural formula reduces to a nocnzow'nmnoncnow .(2).

and should not be construed as limiting in any way. 75.

For example, a diether of theformular shown in (ii at-eve may be prenared'aecordmg to the following equation: a R i110 oiH-flo ,-H acct 1 Z c 2 H-|-V(+ CEAZOR (3) For the case where y is equal to zero, the above equation becomes: 1 sesamercuaiobuwo i Other materials of this classification suitable for the practice of this invention maybe prepared according to Equation 4 from dodecanol, polyoxyethylene glycol of average molecular weight 400, and trioxymethylene; dodecanol, poly'oxyethylene glycol of average, molecular weight 400, and acetaldehyde; hexadeconal, polyoxypropylene glycol of average molecular weight 400, and trioxymethylene; dodecanol, polyoxyethylene glycol of average molecular weight 600, and trioxymethylene; hexadecanol, polyoxyethylene glycol of average molecular weight 1000 and trioxyinethylene; dodecanol, polyoxyethylene glycol of average molecular weight 1000; and trioxymethylene; dodecanol, poly'oxyethylene glycol of average molecular weight 1540, and trioxymethylene; hexadecanol, polyoxyethylene glycol of average molecular weight 1540 and trioxymethylene; hexadeconal, polyoxyethylene glycol of average molecular weight 600, and trioxymethylene'; hexadecanol, polyoxypropylene glycol of average molecular weight 750 and trioxymethylene; hexadecanol, pol'yoxypr'opylene glycol of average molecular weight 1200, and trioxymethylene; dodecanol, polyoxyethylene glycol of average molecular weight 300, and trioxymethylene; hexadecanol polyoxyethylene glycol of average molecular weight 400, and benzaldehyde; dode'canol, polyoxyethylene glycol of average molecular weight 1000 and acetone; dodecanol, polyoxyethylene glycol of average molecular weight 1000and propanal; dodecanol, polyoxyethylene glycol of average molecular wei ht 1000, and butanal; dodecanol; polypropylene glycol of average molecular weight 750, and phenylac'etaldehyde; and hexadecanol, polyoxyethylene glycol of average molec-- ular weight 1400, and methyl ethyl ketone, In general it may be said that suitable compounds will result from the synthesis of Equation 4 where the aliphatic alcohol c'ontains at least about '12 carbon atoms and the polyoxyalkylene glycol contains at least about -7 oxyalkylene groups. The aldehyde or ketone from which the unsubstituted oxymethylene or substituted oxyinethylene group is derived may bechosen from a wide variety of such compounds, as shown by the examples, the principal requisite being that it will not undergo undesirable side reactions under the mildly acid conditions of the method. Thus, such aldehydes as crotonalde- Hyde and furfural undergo polymerization, etc;

(as is more fully explained hereinafter) and the.

yield of desirable diethers is thus reduced.

The synthetic procedure outlined in Equation 3 is especially applicable to low molecular weight alcohols such as methyl, ethyl, and propyl, and is further a convenient way of synthesizing compounds in which R contains an aryl radical; Thus, in Equation 3, if phenoxyethanol or phenylethanol were employed as ROH, theresultingdiether would be aroxyalkyl or aryl, respectively. Diethers of this first classification, containing smaller R groups, are especially suitable for the practice of this invention when their'molecular weight is at least'about 2000 005000.

The second iclasification which may be considered consists of the diethers having'thegencral structural formula L,

RO(CnI-I21iQ)mCE2OR (7') wherein, again, the symbols R, R, E; n, and :1: have the same significance assigned to them hereinbefore. An exemplary method of'prepar ing a compound of this classification may be represented by the equation: Ron +-Ro o,.mn-o)=11+ c1220 a ownmflonomon l x A specific example of a synthesis according to Equation 8 is the following:

C-IHQOHI-CJHBO(CnH2nO):H+HCHO C4 BO(C1| 2O)2CH2OC4HB in which the monoether olrrgotcnmnonnis the monobutyl ether of a polyoxyalkylene glycol containing both oxyethylene and'oxypropylene groups in random arrangement and-in which the weight ratio ofethylene oxide to propylene oxide is approximately 1:1, the molecular weight of the monobutyl ether being approximately'1000; Other specific examples of compounds falling within this classification andsuitable for'the practice of this invention are those which may be preparedaccordingto the reaction of Equation 8 from benzyl alcohol, the monobutyl ether of Equation 9, and trioxymethylene; hexadecanol, the monobutyl ether of a polyoxyethylene glycol of everage molecular weight 750, and trioxymethylene; dodecanol, the monobutyl ether'of Equation 9, and acetaldehyde; octanol, the monobutyl ether of a polyoxypropyleneglycol of aver"- age molecular weight 3000, and acetone; and do-- decanol, the monobutyl ether of a polyoxypropylene glycol of average molecular weight 1000, and benzaldehyde. Infact, the limiting features appear only to be that the total molecular weight of the compound should be at least about 1000 and neither of the groups R. or R should-be smaller than four carbon atoms. With these limitations, compounds prepared: from awwide variety of alcohols, monoethers, and aldehydes or ketones have been found suitable for the prac-- tice of this invention. A third classification which may be considered consists of cliethers of the following structural formula: l i r RO'(CnH2nO') :nCE2O (CnHZnOXzrR- wherein R, R; E, m, and a: have the same significance ascribed to them hereinabove. Specific examples of syntheses according to Equation 10 are the following: j l zoimow uznopn 110110 i CAHQO(GI5 MO)|UH2O(CaHhOfhCxHt J l (i-l) wherein the monoether 'CsiHDO(CnH21lO) wI-Iisthe sai'zjias that described hereinabov'e for Equa- Y canto oimobomowimobcwni {Other suitable compounds falling Within this classification and useful for the practice of this invention include those formed by'aldehyde or lg'etone coupling of monoethers of polyoxyalkylene glycolsof such character that the total'molecular wherein R, R, E, n, a: and 2 have the same significance as heretofore. A specific example of a synthesis leading to a compound of this classification is the following:

wherein the monobutyl ether C4H90(C11H2n0)xH isthe same as described for Equation 9 and the polyoxyethylene glycol HO-(CzHLrOhH is of average approximate molecular weight 6000. f A study of these compounds will reveal that they are related to those of the third classification, above, but instead of merely coupling two monoethers through an unsubstituted oxymethylene or substituted oxymethylene group, as in the compounds of the third classification, in these compounds there has been introduced an additional polyoxyalkylene chain between the two monoethers, by means of the oxymethylene bridges, thus obtaining greater molecular weight and chain length. In general, increased molecular weight contributes to the efficiency of antifoaming materials. As indicated in the discussion of compounds of the third classification, higher molecular weight is especially desirable, and becomes particularly so, when the diethers are to. contain two relatively small groups R and R2. Also, many monoethers of polyoxyalkylene glycols are readily available wherein the polyoxyalkylene chain is relatively short and coupling by meansof the single oxymethylene group, to give compounds similar in structureto those of the third classification would lead to compounds of molecular weight below the lower lim iting value. However, the introduction into the chain of a high molecular weight polyoxyalkylene chainderived from readily available polyoxyalkylene glycols will permit the use of these shorter chain monoethers to yield very efficient antifoam compositions;

.Forexample, many of the methyl and ethyl monoethers of polyoxyethylene and DOIYOXYDIO-r pylene glycols are available commercially, but tlie methyl and ethyl groups are of a size that when R or R is composed of either of them, it is desirable, for efiicient antifoaniactivity, that the intermediate polyoxyalkylene chain be of molecular weight in the neighborhood of at least 2000, swede: somew top si nature or. t e ewe:-

8. kylene groups. The synthesis of Equation 14 mits use of these monoethers}. p

Likewise many monoethers of the type repre-' sented by plienoxyethoxyethanol, 'alkylphenoxy-' ethoxyethanol, and correspondingcompounds in which other oxyalkylene group are inserted in the chain, may readily-be used in thesynthesis of Equation 14. I?

As stated hereinabove, the-synthetic methods already described were chosen as being suitable ones for the preparation of the diethers under discussion..-There are other suitable, methods also and these will readily suggest themselves to one skilled in the art. As a single example of amethod different from the ones described above,

' the following may be cited:

A polyoxyalkylene glycol is converted tothe corresponding di-chloromethyl ether:

ECHO .1

This di-chloromethyl other may then be reacted with an alcohol:

-- I I .aoomownninobcmoa Reference to the preceding :discussion will show that this resulting diether is one falling within the first classification.

hydroxyl-containing molecules,

- Similarly, the di-chloromethyl ether time; tion 15 may be reacted with a monoether: ofa polyoxyalkylene glycol: v

Q d .1 Reference tothe preceding discussion will show that this diether falls into the fourth classification. T Since as alreadystated it is possible. to preparethe diethers of this invention by various routes, the ,invention should not be limited by the an: lowing descriptive discussion which i merely mg tended to illustrate in detail satisfactory pro: cedures for the preparation of the materials} suitable for employmentwithin the scope of the present invention. The preparative methodis; based upon the fact that it is possible to linktogether two hydroxylcontaining molecules byl meansof a condensation with an aldehyde or a ketone whereby one molecule of water is elimil' nated with the formation of a methylene bridge between the oxygen atoms of the aforementioned Conditions favoring this condensation are those which-favor the removal of water from the reaction zone. Acid catalysts may also be employed, suitable examples of which are, sulphuric acid, hydro chloric acid, ferric chloride, aluminum chloride, stannic chloride, and zinc chloride. v The result ing formals, or substituted formals, are. unstable in the presence of the acidic catalysts and, there; fore; prior to tharecovery of the product Us desirable to neutralize the acidic catalyst wiith some'caustic material such as caustic soda oda hastened and made more complete by operating under a vacuum or; with gasification-of the reacting mixture e. g. by a stream of air, nitrogen,- carbon dioxide or other suitable inert gases), It i preferably carriedout through the use ofa vola l inert wh a such" benz ne .1 was a qaaee distillate being recovered and permitted to sepa rate into two phases, the upper solvent phase 'being continually returned to the reaction vessel and the lower aqueous phase being discarded :Irom the separator.

Following th above suggestions, the reaction of Equation 6 hereinabove is effected by heating the mixture of 2 moles of, hexadecanol, 2 moles of trioxymethylene and 1 mole of commercial .nonaethylene glycol in the presence of an approximately equal'weight of benzene and with the V additionof solid ferric chloride in a quantity equal to approximately 0.5% of the combined weight of the alcohol, glycol and aldehyde. Heating is carried. outso that the benzene slowly distills from thereaction mixture carrying with it the waterformed; 'The distillateiis collected in a conventional water trap, the waterseparated and the benzene returned to the reaction vessel. When thecwater collected is equivalent to the theoretical amount expected. from the reaction, the

acidic catalyst (ferric chloride) is neutralizedby the addition of a slight excess of solid, pulverized sodium acetate and the benzene is distilled leaving the reaction product behind as aviscous liquid which tends to partially solidify 'upon cooling. If desired, the product may be filtered while but.

In general the above mode of operation, using approximately the stoichiometrical quantities of reactants, may be applied to the preparationof any of the compounds described hereinabove. Theacid catalysts maybe used in airange of 0.3 to 1.0% by weight based on the totalweight-of the "reactants exclusive of any dehydrating solvent. The dehydrating solvent may be chosen from a variety of such solvents and by varying theboiling point and the'pressure under which the reaction is carried out these reactions may befefiected at any temperature within the range of about50 to 150 C. Frequentlybecause of some loss of aldehyde or ketone during the disti1latiori,-it is desirable to use a slight excess of this reactant and 'insome cases to add it portion-wise to thereaction mixture. Furthermore, in carrying out a reaction of the type illustratedin Equation 3, it is desirable to addthe alcohol (ROH) after the reaction between the aldehyde orketone and the 'polyoxyalkylene glycol has proceeded for some time. l I

the feedwater by means of additional dispersing agents, as described below. All of the products exhibit substantial ,in'solubility in hot water, the

phenomenon of decreasing solubility in water with increasing temperature being characteristic ofcompounds of this class which contain multipleifethe'r linkages and in which' theratio of ether linkages to carbon is sufficiently great to permit the weak hydrogen bonding effect of the ether oxygen to confer water solubility. I .The amounts of an .antifoam agent employed in inhibiting the foaming of water in a 'steam generator will depend upon several factors, among them the per cent of solids in the foaming liquid,

10 the nature of the solids, the alkalinity, tempera ture, and pressure, the type and degree of circulation in thesteam generator, the rate of steam production, and the amount of foam suppression desired. It is, therefore, impossible to state any rigid rules for estimating the amount of an antifoam whichneeds to be used. The amounts of the diethers of this invention which are required are, however, extremely small; For many purposes, amounts of the order of 0.01 grain per gallon to 0.02 grain per gallon in the feedwater are sufficient, and under certain conditions quantities as low as 0.001 grain per gallon "in the'feedwater have proved effective. In general, it can "be said that quantities greater thanOJ grainper gallon in the feedwater would seldombe'required.

By way of illustrating the remarkable effectiveness of the diethers of this invention, the method of testing their antifoam efiiciency in the laboratory will be described and exemplary data given. z

In the laboratory, the experimental {boiler used was of the type described in the publication Solid Matter in Boiler Water Foamingfl j by Foulk and Brill, which appeared in the periodical Industrial and Engineering Chemistry, volume'2'7, pages 1430-35. This boiler was fitted with sight glasses on each side of the steam release space so that conditions in the boiler in a zone several inches above and below the. normal waterlevel were observed while the boilerwas operating under pressure. It was also equipped with an automatic water level control which held the water level within a range of $0.25 inch.

In the seriesof experimentsdescribedfbelcw, a feedwater was used having the following composit-ion, expressed in parts. per million, lay-weight:

Calcium hardness (as CaCOs) 1'54 -.o Magnesium hardness (as CaCOs) "154.0 Alkalinity (methyl orange) (as CaCO'slH 'ZZSQ Sodium chloride (as NaCl) 35.5 Sodium sulfate (as NaZSOi) 718.0 Tannin extract, dry -g 3412 To this feedwater was added the antifoamtcomposition ofv the character and the'vquanti'ty specified in the specific experiment, and :thiswater was then gradually concentrated in the test boiler by evaporation at the rate of six gallons perhour at 250 pounds per square inch (p. s; 1.) gauge pressure. A continual recording was made of the relative conductivity of the condensate from the boiler, and continual observations were made of the character of the boiling ,andithie amount of foaming as seen through thesi'ght glasses. When the antifoam thus introduced continuously with the feedwater was no longer able to overcome the foaming tendeniesbrought about by the concentration of dissolyed'solids 'i 'the boiler water, the foam height becamegreat enough to cause boiler water to be .carried out of the boiler with the steam, .and this end-point of the. test was determined both by observation through the sightglasses and, particularly, by the abrupt increase in the conductivityof the steam, as shown in-thecontinuous recorder; At,=:this endepoint, asample of the boiler water was withdrawn from the boiler and ana1yzed,:a-nd the effectiveness of the antifoam expressed in terms of the total dissolved solids concentration which .it permitted the boiler to carry. Ahigh value of total dissolved solids (TDS) indicates an effective anti-foam; With no antifoam, thisfeedwater gives a carryover at a total dissolved. solids value of=approximately grains per gallon. f

, 1 11 Test] "An: antifoam composition was ,preparedby the reaction of apolyoxyethylene glycol ofaverage .molecular weight 900, octyl' alcohol, and -trioxymethylene in a molecular ratio of 6:1:6, using a;,dosageof 0.005 grain per gallon. Carryover .didnot occur until the total dissolved solids concentration in the. boiler water had reached 3637 grains pergallon. The active antifoam; ingredient'is believed to have a structure represented by Formula, 1 above. 1

, Test IIv A compound corresponding to the general for- ;c1'f dipropylene glycol andgrindin the resulting liquid mixture into 95 grams of a dry, pulverized 'lignin, derivative commonly used in boiler water treatment, and made by desulfonation and partial depolymerization of sodium lignin sulfonate by treatment with aqueous alkali at high tem- "peratures'. This material exhibits an excellent dispersing effect on the diethers but neither it,

-nor the oleic acid or dipropylene glycol. of themsaves, exert an antifoam effect in the boiler. The dry, pulverized antifoam composition, con- ;taining 3% of the diether, was added to the feed- ;water at a dosage of 0.167 grain per gallon, re-

sulting in aconcentration of the diether in the feedwater of 0.005 grain per gallon. This per- -mitted av total dissolved solids concentration in the boiler of 274'? grains per gallon before carryover occurred.

Test III A compound of the type represented by Formula 7, above, was prepared from benzyl alcohol, trioxymethylene, and the monobutyl ether of a polyoxyalkylene glycol containing both oxyethylem and oxypropylene groups in the chain in a weight ratio of approximately 1:1, and having a a total average molecular weight of about 1000.

The mole .ratio of the three reactants was 1:1:1.

When finished, the product was a liquid which :was' formulated into a dry-appearin pulverized composition exactly as was done in the case of jth'e diether of Test II. The pulverized composition, containing 3%, by weight, of the diether, "was'a'dded tothe feedwater at a dosage of 0.167 grain per gallon, resulting in a concentration of the diether in the feedwater of 0.005 grain per gallon. This permitted a total dissolved solids concentration in the boiler water of 558 grains pergallonbefore carryover.

Test IV A compound of the type represented by For- -mula 10, above, was prepared by reacting two -molecular portions of the monobutyl ether dez'scribedjin Test III with one molecular portion of trioxymethylene in boiling benzene, in the presence of a small amount of ferric chloride as bat-a- ,lyst. The resulting diether was a liquidand'was mixed with dipropylene glycol and the lignin derivative of Test II in a weight ratio of 321296, respectively. The resulting pulverizedcomposi tion, containing 3%, by weight, of the diether, was added to the feedwater in a dosage of 0.167 grain per gallon, resulting in a concentration-of the diether in the feedwater of 0.005 gr'ain'per gallon. This permitted a total dissolved'l solids concentration in the feedwater of 697' grains per gallon before carryover. I

Test V l A compound having the" structure represented by Formula 13, abovejwas preparedfrom the monobutyl ether described in Test III, a polyfoxyethylene glycol of average molecular weight 6000 ("Carbowax 6000), and trioxymethylene in a molecular ratio of 2:1:2, respectively,.' using henzene and ferric chloride. The diether, when finished, was a light brown wax,'soluble-1in cold water' It was added to the feedwater. ata'dosage of 0.005 grain. per gallon, and permitted; a total dissolved solids'concentrationin the boiler .in excess of 3198 grains per gallon, the test being stopped with nocarr'yover.

One of the difficulties of using most antifoam materials is that of conveniently introducing them into the water in small; controlled amounts so that their maximumv efiectiveness is utilized. While many of the diethers employed in accordance with this invention are readily soluble incold water, others are not completely soluble and must be rendered readily dispersible for use. Liquids, waxes, and preformed emulsions are inconvenient to apply to the 'feedwaters used by locomotives and other power plants. It is thusa further object ofthis invention "to provide the diethers compounded with other water treating chemicals in a powdered or briquetted form which can readily and conveniently be addedto water,:a nd which will dispersein the water quickly without excessive agitation or mixing.

The diethers employed'in the practice of this invention can all be incorporated into dry powdered materials'such as powdered tannin s d-ium lignin sulfonate, the desulfonated lignin described in Test II hereinabove, soda ash, various ,orthophosphates and polyphosphates, Dependscribed are readily and completely dispersible in water when the diethers themselves are soluble'or dispersible,

give dry-appearing compositions by the method described if a dispersing agent is'used in conjunction with them. In fact, many of the common water treating chemicals of a1 tannin or lignin nature behave as sufiiciently-powerfuldisvpersants to readily disperse the insoluble diethers inthe form of a relatively stable aqueousdispersion. Where it is not desired to use the tannins or lignin derivatives in quantity sufiicient to act as dispersants for the. diethers, a small'amount of soap, such as the alkali metal soaps of 0 916 acid or tall oil, or a sulfonated oil, may be employed with good results, and the amount of soapfor'sul- -fonate thus required is'insuflicie'nt to interfere When diethers are employed which 'aresubstantially insolublein water, these, too,

with the powerful antifoal'n effectof the. diethers or to render" the boiler compound dirty.

In generaLthen, the diethers of this invention may be prepared 'in'the form of dry-appearing pulverized or briquetted compositions which are readilyand completelydispersible.in water with aminimum of agitation by .incorporating them, with or Without a dispersant such as soap or sulfonated oil, with various tannins, li nins, or other piulverized chemicals, either alone or combina- The practice of the invention is applicable to the inhibition of foaming in steam generation over a relatively wide pressure and temperature range. In locomotive boilers, steam is enerally generated at pressures around 250 pounds per square inch and the corresponding temperatures. Excellent results have been obtained with the practice of the invention at pressures within the range of 100 to 300 pounds per square inch and the corresponding temperatures. Thein-vention canlalso be used, however, in connection with the generationof steam at much higher pressures and the corresponding temperatures, as,for example, in stationary boilers operating at pressures as highas 1000 to 1500 pounds per square inch. The compositions employed in accordance with the invention are effective not only in inhibiting foaming butalso in conditioning and improving the quality of the steam. For this purpose, they may :be used in evensmaller amounts than the amounts required .for the complete inhibition of foaming and priming. l

The diethers employed in the practice of this invention are desirably used in conjunction with other organic water treating chemicals of the tannin and lignin types in treating many water supplies as will be seen from the following. On waters high in magnesium salts in which the magnesium in the boiler will generally be in the formof magnesium hydroxide, it is desirable that sufficient of hydroxylatedforganic material such as tannins, tannic acid,f gallic acid, pyrogallol, catechol, phloroglucinol, etc. be added along with the diethers. These hydroxylated organic compounds havethe ability ofmullifying the bad effects of the magnesium; hydroxide. Magnesium hydroxide appears to. partially selectively adsorb the antifoa'm material and. so take it out of the boiler water so that the fullantifoam action cannot be exerted by the antifoam compositions when in this adsorbed state. However, when an organic material such as a tannin is added, magnesium hydroxide appears to lose its ability to interfere with the. antifoam action. Inasmuch as most boiler feedwaters encounteredwi'll have varying amounts of magnesium salts present, it is desirable *thatsuch hydroxylated organic compounds be mixed'with the diethers prior to addition to the boiler feedwater.

Thus another advantage is evident in preparing and using the pulverized or briquetted compositions hereinabove describedcontaining both the diether antifoam and the polyhydroxylated organic material of the tannin or lignin-derivathe type. t I

As will be apparent from the foregoing description', the' compounds employed in accordance withthe invention do'notallgive the same results and from that standpoint are not necessarily equivalents. Some of these diether compositions, especially those of the type referred to in Test I, are truly remarkable in their foam inhibiting properties even when compared with the bestof the antiioam compositions which have been previously used commercially.

114 The term an "oxymethylene group unless modified by the words unsubstitilted" or substituted is intended to cover generically the group 7 t -o-cwhere A and'B may be hydrogen or carbon radicals, e. g., alkyl or aryl radicals. An unsubstituted oxymethylene group is one in which both A and B are hydrogen atoms. A substituted methylene group is one in which A or 3B or both is a carbon radical in which a carbon'atomjis linked to the main methylene group.

,A preferred class of compounds for employ,- ment in accordance with the invention is that derived by the reaction of an aldehyde or 'a ketone with a 'monohydric alcohol and a. member from the group consisting of monoethers of p0lyoxyalkylene 'glycols and polyoxyalkylene glycols, wherein the compound is at least partially soluble in water at room temperatures of'say F. and decreases in solubility to substantially water insolubility upon heating to steam generating temperatures.

The invention is hereby claimed as follows:

1. .A process of minimizing the production of foam in and the priming of steam generators opcrating under superatmospheric pressure conditions which comprises incorporating with a water therein containing an amount of total solids tendingto produce foaming and priming a minor quantity of a diether of a poiyoxyal'kylene glycol characterized by a total average molecular weight of at least 500and a chemical structure inwhich the polyoxyalkylene chain contains at least one oxymethylene group, said diether being substantially insoluble in said water under said steam generating conditions and said quantity being sufficient substantially to inhibit foaming and priming. p

2; A process asclaimed in claim "1 in which the quantity of saidpolyoxyalkylene glycol incor porated into the water is-Witl'liri the range of 0.001 grain to 0.1 grain per gallon of water.

3. .Aproce'ss as claimed in claim 1 in which the steam is generated at pressureswithin the range of .100. to 1500 pounds per square inch and the corre pondingtemperatures.

4,. A process as claimed in claim 1 in'whjich a steamis. generated at pressures within the range of to 300 pounds per square inch and'thecorrespondingtemperatures.

5. A process of minimizing the production of foam in and the priming of steam generators operating under superatmospheric pressure condi tions which comprises incorporating with'a water therein containing an amount of total solids tending to produce foaming and priming a quantity of a diether of a polyoxyalkylene glycol characterized vby an average molecular weight of at least 500], and a chemical'structure in which the polyoxyalkylene chain contains atleast one unsubstituted oxymethylene group and higher oxyalkylene groups havingnot more than three carbon atoms, said diether being substantially insoluble in said water under said steam generating conditions and said quantity being sufficient substantially-to inhibit foaming and priming. 6. A process of minimizing "the production of team in and the priming of steam generators operating under superatmospheric pressure conditionswh-ich comprises incorporating with a. we'- ter'therein containing an amount of total solids 1s tendingto produce foaming and priming'a quantity of a diether of a polyoxyalkylene glycol having the following structural formula:

wherein R and R are'from the group consisting of alkyl, aryl and aralkyl, E is from the group consisting of hydrogen, alkyl and aryl, n and a: are integers of at least 2, y is from the group consisting of an integer, and the average molecular weight is at least 500, said diether being substantially insoluble in said water under said steam generating conditions and said quantity being suflicient to substantially inhibit foaming and priming. 1

7. A process 'of minimizing the production of foam in and the priming of steam generators operatingunder superatmospheric pressure conditionswhich comprises incorporating with. a water therein containing an amount of total solids tending to produce foamingand priming a quantity of a dialkyl ether of a polyoxyalkylene glycol containing in the polyoxylalkylene chain at least two, unsubstituted oxymethylene groups anda plurality of larger oxyalkyl-ene groups, the number of carbon atoms in the terminal alkyl ether groups not exceeding 4 and thevaverage molecular weight of said dialkyl ether deriva tives-being within the range from 2000 to 5000, said quantity being sufiicient to substantially inhibit foaming and priming.

;.8.;A process of minimizing the production of foam in and the priming of steam generators op- ,erating under superatmospheric pressure conditions which comprises incorporating with a, water therein containing an amount of total solids tending toproduce foaming and priming 0.001 to. 0.1 grain per gallonof said water of the productofthe reaction at temperatures wihtin the not of th-ereaction at temperatures within the elimination of water of 2 moles of an aliphatic alcohol containing at least 12 carbon atoms, 1 molof .a polyoxyalkylene glycol containing at least Yoxyalkylene groups fromlthe group consisting of oxyethylene and oxypropylene groups,

7 and 2 moles of formaldehyde.

. 9. A process of minimizing the production of foaming in and the priming of steam generators operating under superatmospheric pressure conditions which comprises incorporating with a water therein containing an amount of total solids tending to produce foaming andpriming alquan'tit'y of a diether of a polyoxyalkylene glycol -having the general iormula i I RO(CnH2nO) ICEZOR' wherein Rand R are from the group consisting of alkyl, aryl and aralkyl, neither R nor R con--. taining, less than 4 carbon atoms, E is from the group consisting of hydrogen, alkyl and aryl, n and a; are integers of at least 2, and the average molecular weight is at least 1000, said diether being substantially insoluble in said waterunder said steam generating conditions, and said quan-- tity being within .the range of 0.001 to 0.1 grain per "gallon of water treated.

l0.' Aprocess of minimizing the production of foam in and the priming of steam generators operating under superatmospheric pressure con-I ditions which comprises incorporating with a water therein containing an amount of total solids tending to produce foaming and priming 0.001 to 0.1 grain per gallon of said water of the product of the reaction at temperatures within the rag of 50 d sm sf i e es .C- th the elimination of water of 1 mol'of an: alcohol containing at least-4 carbon atoms, 1 mol of a monoalk'yl ether of a polyoxyalkylene glycolin which the said monoalkyl group contains at least 4 carbon atoms'and the polyoxyalkylene chain contains both oxyethylene and oxypropylene groups in random arrangement and in the weight ratio of ethylene oxide to propylene oxide of a'p' proximately'lzl, and 1 mole of formaldehyde;

11. A process of minimizing the production of foaming in and the priming of steam gener ators operating under superatmospheric pressure conditions which comprises incorporating with water therein from which the steam is generated a minor quantity of a diether of a poly'oxyalk'yl ene glycol having the following general formula wherein R and R are from the group consisting of alkyl, aryl and aralkyl, E is from the group consisting of hydrogen, alkyl and aryl, n. and 2': are integers of at least two and the 'average molecular weight is at least 1000, said. diether being substantially insoluble in said water under said conditions of steam generation,- and said quantity being sufiicient to substantially inhibit foaming-and priming. i

12. A process of minimizing the production of foaming in and the priming of steam generators operating under superatmospheric pressure 'conditions which comprises incorporating withwa ter therein from which the steam is generated a minor quantity of a diether of a polyoxyalkyl ene glycolhaving the general formula 1 Bo curiae);0mmonmnononmonmnox R' wherein R. and R? are from the group consisting of alkyl, aryl and aralkyl, E is from the group consisting hydrogen, alkyl and aryl, and n, :c. and a are integers of at least 2, said diether having an average molecular weight of at least 500 and being substantially insoluble in said water under said .conditions of steam generation, andsaid quantity being suflicient to substantially inhibit forming. and priming.

13. A process of minimizing the production of foam in and the priming of steam generators operating under superatmospheric pressure conditions which comprises incorporating with a water therein containing an amount of total solids tending to produce foaming and priming 0.001 to 0.1 grain per gallon of said'water of the product of the reaction at'temperatures with inthe range of 50 degrees C. to degrees ,C. with the-elimination of waterof 2 .moles of a monoether of a polyoxyalkylene glycol, 1 mole of a polyoxyalkylene glycol and 2 moles of formaldehyde, the oxyalkylene groups in said monoether and said polyoxyalkylene glycol being from the group consisting of oxyethylene and oxypropylene. groups, said quantity being suflicient to substantially inhibit foaming and priming. 14. A method of generating steam from a boiler water having a tendency to foam'on boilingand which contains magnesium compounds, which comprises dispersing in said watera (luautity .ofa diether of a polyoxyalkylene glycol characterized by .a total average molecular weight of at l-east 500 and achemical structure in which the polyoxyalkylene chain contains at least one oxymethylene group, said diether being substantially insoluble in said water under steam generating conditions, and a quantity of a. hydroxylated organic compoundlfrom the group consisting of tannins, sodium lignin sulfonate land desulfonated effective to nullify the 15. The method of generating steam from a boiler water having a tendency to foam on boiling and which contains magnesium compounds, which comprises dispersing in said water a quantity of a diether of a polyoxyalkylene glycol characterized by an average molecular weight of at least 500 and 'a chemical structure wherein the polyoxyalkylene chain consists of at least one oxymethylene group and higher oiwalkylene groups having not more than 3 carbon atoms, said diether being substantially insoluble in said water under steam generating conditions, and a quantity of a hydroxylated organic compound from the group consisting of tannins, sodium lignin sulfonate and desulionated lignins eii'ective to nullify the action of the magnesium compounds on said diether, the quantity of said diether being effective to inhibit the tendency of said water to team on boiling, and heating the resultant aqueous dispersion to the boiling point. 25 2,442,768

l8 16. The process 01 generating steam from a water having a tendency to foam on boiling which comprises dispersing in said water a quantity of a dialkyl ether of a polyoxyalkylene glycol containing in the polyoxyalkylene chain at least one oxymethylene group and a plurality of larger oxyalkylene groups from the group consisting. oi oxyethylene and oxypropylene, said dialkyl other being substantially insoluble in said boiler water under steam generating conditions. the average molecular weight of said dialkyl ether derivative being at least 500 and said quantity beingeffective to inhibit the tendency of said water to foam on boiling, and heating the resultant aqueous dispersion to the boiling point.

' CARL E. JOHNSON.

REFERENCES CITED The vfollowing references are of record in the file of this patent: 1 UNITED STATES PATENTS Number- Name Date 2,425,042 McNamee et al Aug. 5, 1947 Gunderson June 8, 1948- 

1. A PROCESS OF MINIMIZING THE PRODUCTION OF FOAM IN AND THE PRIMING OF STEAM GENERATORS OPERATING UNDER SUPERATMOSPHERIC PRESSURE CONDITIONS WHICH COMPRISES INCORPORATING WITH A WATER THEREIN CONTAINING AN AMOUNT OF TOTAL SOLIDS TENDING TO PRODUCE FOAMING AND PRIMING A MINOR QUANTITY OF A DIETHER OF A POLYOXYALKYLENE GLYCOL CHARACTERIZED BY A TOTAL AVERAGE MOLECULAR WEIGHT OF AT LEAST 500 AND A CHEMICAL STRUCTURE IN WHICH THE POLYOXYALKYLENE CHAIN CONTAINS AT LEAST ONE OXYMETHYLENE GROUP, SAID DIETHER BEING SUBSTANTIALLY INSOLUBLE IN SAID WATER UNDER SAID STEAM GENERATING CONDITIONS AND SAID QUANTITY BEING SUFFICIENT SUBSTANTIALLY TO INHIBIT FOAMING AND PRIMING. 